1. Field of the Invention
The present invention relates to a surface-mount coil package for use, for example, in an EL (electroluminescence) drive circuit, an LED (light-emitting diode) drive circuit, or a DC power circuit, and also relates to a method of producing the same.
2. Description of the Related Arts
A drive circuit for turning on an EL or an LED, or a DC power circuit uses a small-sized coil formed by winding a conductor around a bobbin made of a magnetic material, e.g. ferrite (see Japanese Patent Application Publication No. 2003-77738). In a thin compact electronic device, such a circuit used therein generally adapts a surface-mount coil package that includes a small-sized coil and its associated IC devices mounted on a circuit board (see Japanese Patent Application Publication No. 2004-336950).
FIG. 11 is a sectional view of a conventional small-sized coil 81. The coil 81 includes a bobbin 82 made of a magnetic material, and a winding 88 wound around the bobbin 82. A pair of terminal electrode plates 86 and 87 is secured to the bottom of the bobbin 82. End portions 88a and 88b of the winding 88 are wound around and soldered to the terminal electrode plates 86 and 87, respectively. When the coil 81 is mounted on a circuit board, the terminal electrode plates 86 and 87 are soldered to a wiring pattern on the circuit board.
FIG. 12 illustrates a part of an apparatus, whereby the bobbin 82 is gripped and rotated so that a conductor is wound around the bobbin to form the winding 88. Specifically, the apparatus has a spindle 61 and a chuck 91 secured to the spindle, the chuck having a pair of jaws 91a for gripping the bobbin 82 therebetween.
The gripped bobbin 82 has the electrode plates 86 and 87. The leading end of the conductor is wound around one of the electrode plates 86 to form a starting end 88a of the winding 88 of the coil 81. The spindle 61 is then rotated to rotate the bobbin 82, thereby winding the conductor around the bobbin 82 to form the winding 88. After the winding 88 is formed, a terminating end 88b of the winding 88 is wound around the other electrode plate 87. The conductor is then severed from the winding 88. The bobbin 82 with the winding 88 is removed from the chuck 91, and the starting and terminating ends 88a and 88b of the winding 88 are soldered or welded to the electrode plates 86 and 87, respectively. This completes forming of the coil 81.
To form the surface-mount coil package, the coil 81 and its associated IC devices (not shown) are mounted on a surface of a circuit board, the surface being formed with a wiring pattern. The coil 81 and the IC devices on the circuit board are then encapsulated with resin. Japanese Patent Application Publication No. 2004-336950 discloses a method of producing such a surface-mount coil package. According to this method, a substrate is formed with a multiplicity of wiring patterns. The wiring patterns are arranged in series in the X and Y directions. Sets of IC devices including a coil are mounted on and electrically connected to the respective wiring patterns. The resulting assemblies are encapsulated with resin. Thereafter, the substrate is cut to provide individual surface-mount coil packages each including a circuit board with the circuit pattern and the coil and the IC devices on the circuit board.
The method is suitable for use in mass production of coil packages. However, it needs a large number of coil winding machines, resulting in an increase in the cost of equipment. Further, it requires mounting/dismounting operation of coils in connection with the winding machines and, thus, increases the production time and cost of coils.